1. Field of the Invention
The present invention relates to providing signaling byte resiliency in telecommunication networks.
2. Description of Related Art
In conventional telecommunications network, many protection applications use signaling bytes to indicate the state of the protection application and to also request various protection actions. These signaling bytes conventionally traverse the network in the signaling overhead of an optical transport frame such as a synchronous optical network (SONET) frame. As these bytes traverse the network, they can be corrupted by conditions on the physical medium or by the intermediate telecommunications equipment. Standard signaling byte mechanisms may accept these corrupted bytes, causing the protection application to act on signaling bytes that are invalid.
Many conventional protection applications use signaling bytes to indicate the state of the protection application and request various protection action. In SONET and synchronous digital hierarchy (SDH) networks, signaling bytes are usually provided within a frame. The standard frame contains a variety of information and provides the information at unique locations within the frame. The frame includes an overhead section and a payload section. The payload contains the information to be transmitted while the overhead contains information such as framing, error monitoring, management and payload pointer information. The overhead is sectioned into three areas, path overhead, line overhead and section overhead. Contained within the line overhead are byte locations that may be used to store signaling information. For example specific byte locations known as K1 and K2 bytes may be used. The K1 and K2 bytes are often referred to as the K-bytes and signal or trigger protection mechanisms.
In optical networks, such as SDH and SONET, when a frame of data is received at, for example, a node, the data contained within the various byte locations within the overhead are used by the various components in the node in order to process the data properly. According to the SONET networks standards described in the Bellcore GR-253-CORE, hereby incorporated by reference, a standard filter is used within each node to determine the accuracy of the received data contained within certain byte locations. For K-bytes if the standard filter determines the k-bytes are consistent for three frames and contain a valid bit pattern, then they are accepted. A similar type of filter may be used in SDH applications.
However, conditions on a fiber optic cable connecting two nodes, or the intermediate transmission equipment between the two nodes may corrupt the K1 and K2 bytes such that the K-Bytes are consistently incorrect for three frames but also contain a valid bit pattern. For example, they can be corrupted by conditions on the physical medium or by the intermediate telecommunications equipment. Examples include, but are not limited to, intermediate WDM (wave division multiplexing) transport equipment, intermediate Mux/Demux equipment, and facility signal level at or near the LOS (loss of signal) threshold. Standard signaling byte mechanisms may accept these corrupted bytes, causing the protection application to act on signaling bytes that are invalid. Thus, these corrupted signaling bytes are accepted by the network as valid bytes, which may cause significant errors in the system.